1. Field of the Invention
The present invention relates to medical devices and more specifically to implantable medical devices.
2. Description of the Related Art
There are a variety of medical devices that sense data, provide diagnostic information, and/or deliver therapy. When such a device is implantable (in whole or in part), it is referred to as an implantable medical device (IMD). In the present application, IMD refers to devices that sense cardiac events and deliver pacing therapy. Such devices may or may not also include other functions such as defibrillation therapy (e.g., implantable cardioverter defibrillator (ICD)), other monitoring capabilities, alternate cardiac therapies, or non-cardiac monitoring and/or therapies. Thus, the term pacemaker may be used interchangeably with IMD in the present context with the understanding that either term may refer to a device with capabilities beyond those required of a pacemaker alone.
Recently, there has been a recognition that intrinsic conduction and ventricular depolarization, even if somewhat prolonged, is preferable to ventricular pacing; particularly pacing in or near the right ventricular apex. In general, this preference results from the unnatural propagation of a depolarization wavefront that is generated from such a pacing pulse (as compared to intrinsic depolarization).
Previous pacing modes tend to operate at one extreme or another. For example, in a true, single chamber AAI/R device, atrial pacing and sensing is possible, but no ability to provide ventricular pacing (or sensing) exists. On the other hand, DDD/R has historically been the default selection for dual chamber devices. The DDD/R mode will operate to maintain AV synchrony; however, the AV delay is such that intrinsic conduction is precluded in most cardiac cycles. This results in ventricular pacing in a very high percentage of cardiac cycles.
The present assignee has developed new modes that promote intrinsic conduction and are referred to herein generally as ventricular pacing protocols (VPP). One such VPP is Managed Ventricular Pacing™ which is commercially available. A variety of VPP embodiments have previously been described, for example, as in U.S. Pat. No. 6,772,005, issued Aug. 3, 2004, to Casavant et al.; U.S. application Ser. No. 10/246,816, filed Sep. 17, 2002, now U.S. Pat. No. 7,130,683 issued Oct. 31, 2006; U.S. application Ser. No. 10/755,454, filed Jan. 12, 2004, now U.S. Pat. No. 7,218,965 issued May 15, 2007; U.S. application Ser. No. 10/850,666, filed May 21, 2004, now U.S. Pat. No. 7,245,966 issued Jul. 17, 2007; U.S. application Ser. No. 11/115,605, filed Apr. 27, 2005, now U.S. Pat. No. 7,738,955 issued Jun. 15, 2010; U.S. application Ser. No. 11/096,436, filed Mar. 31, 2005, now U.S. Pat. No. 7,881,793 issued Feb. 1, 2011; U.S. application Ser. No. 10/814,692, filed Mar. 31, 2004, now U.S. Pat. No. 7,254,441 issued Aug. 7, 2007; and U.S. application Ser. No. 10/971,686, filed Oct. 25, 2004, now U.S. Pat. No. 7,248,924 issued Jul. 24, 2007, which are herein incorporated by reference in their entirety.
As a generalized explanation, a VPP operates in an atrial based pacing mode to promote intrinsic conduction. Ventricular events are sensed and as long as a ventricular event is sensed in a given cardiac cycle (e.g., A-A interval) the device continues to operate in the atrial based pacing mode. This allows for ventricular sensing during the entire A-A interval. Conversely, if there is no ventricular event, the device provides a ventricular backup pace in the subsequent cycle, timed from the atrial event (paced or sensed) that initiates this cardiac cycle. Thus, in a VPP it is possible to have an entire cardiac cycle devoid of ventricular activity while ultimately maintaining AV synchrony. There are, of course, many variations and embodiments provided that are not described herein for the sake of brevity. It should be appreciated that operation in an atrial based pacing mode includes mode switching a device into such a mode (e.g. AAI/R, ADI/R) and into a mode that provides ventricular pacing or alternatively, operation in a complex mode that includes more comprehensive behavior (e.g., FIDDI).
One benefit of the VPP is that the protocol may be initiated with patients regardless of the status of their AV conduction. Those having intact or partially intact conduction will benefit in that conduction is promoted and ventricular pacing is reduced or eliminated. For those patients with heart block, the VPP will quickly move to provide ventricular pacing and periodically check to determine if conduction has returned. Both in initially recognizing the need to pace and performing the conduction checks, the methodology employed is transparent to the patient.
As previously indicated physicians implanting a dual chamber device often utilize nominal settings and program the device to DDD/R due to its simplicity. The VPP allows for the same type of comprehensive reliability across patient profiles and without the need to program numerous parameters upon implant. The VPPs are preferable in that that they reduce or minimize ventricular pacing when intact conduction is present.